Systems and methods for latency based data recycling in a solid state memory system

ABSTRACT

Systems and method relating generally to solid state memory, and more particularly to systems and methods for recycling data in a solid state memory. The systems and methods include receiving a data set maintained in a memory device, applying at least one iteration of a data decoding algorithm to the data set by a data decoder circuit to yield a decoded output, counting the number of iterations of the data decoding algorithm applied to the data set to yield an iteration count, and recycling the data set to the memory device. The recycling is triggered based at least in part on the iteration count.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to (is a non-provisional of)U.S. Pat. App. No. 61/892,249 entitled “Systems and Methods for LatencyBased Data Recycling in a Solid State Memory System”, and filed Oct. 17,2013 by Cai et al. The entirety of the aforementioned provisional patentapplication is incorporated herein by reference for all purposes.

FIELD OF THE INVENTION

Systems and method relating generally to solid state memory, and moreparticularly to systems and methods for recycling data in a solid statememory.

BACKGROUND

Data in a solid state storage device decays over time requiring moreerror correction capability over time. To correct additional errors,enhanced error correction circuitry may be employed. However, suchenhanced error correction circuitry increases access latency.

Hence, for at least the aforementioned reasons, there exists a need inthe art for advanced systems and methods for maintaining data in a solidstate storage device.

SUMMARY

Systems and method relating generally to solid state memory, and moreparticularly to systems and methods for recycling data in a solid statememory.

Various embodiments of the present invention provide data processingsystems that include: a memory device, a data decoder circuit, and arecycle control circuit. The memory device is operable to maintain adata set, and the data decoder circuit is operable to apply one or moreiterations of a data decoding algorithm to the data set accessed fromthe memory device to yield a decoded output, and to provide an iterationcount indicating a number of iterations that the data decoding algorithmwas applied to the data set. The recycle control circuit is operable torecycle a read data corresponding to the data set. The recycle istriggered based at least in part on the iteration count.

This summary provides only a general outline of some embodiments of theinvention. The phrases “in one embodiment,” “according to oneembodiment,” “various embodiments”, “one or more embodiments”,“particular embodiments” and the like generally mean the particularfeature, structure, or characteristic following the phrase is includedin at least one embodiment of the present invention, and may be includedin more than one embodiment of the present invention. Importantly, suchphases do not necessarily refer to the same embodiment. Many otherembodiments of the invention will become more fully apparent from thefollowing detailed description, the appended claims and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE FIGURES

A further understanding of the various embodiments of the presentinvention may be realized by reference to the figures which aredescribed in remaining portions of the specification. In the figures,like reference numerals are used throughout several figures to refer tosimilar components. In some instances, a sub-label consisting of a lowercase letter is associated with a reference numeral to denote one ofmultiple similar components. When reference is made to a referencenumeral without specification to an existing sub-label, it is intendedto refer to all such multiple similar components.

FIG. 1 shows a solid state storage device including an iterative countbased data recycle control circuit in accordance with variousembodiments of the present invention;

FIG. 2 depicts one implementation of an iterative data processingcircuit that may be used in relation to embodiments of the presentinvention; and

FIGS. 3a-3c are flow diagrams showing a method for iteration count baseddata recycling in accordance with some embodiments of the presentinvention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

Systems and method relating generally to solid state memory, and moreparticularly to systems and methods for recycling data in a solid statememory.

Various embodiments of the present invention provide solid state memorysystems that include an iterative data processing circuit. Where dataaccessed from a solid state memory includes one or more errors, theiterative data processing circuit applies one or more iterations of adata decoding algorithm in an attempt to correct any errors. The numberof iterations required to correct the errors is provided to an iterativecount based data recycle circuit. Iterative count based data recyclecircuit determine whether to recycle the accessed data to increase thereliability of the accessed data and/or decrease the latency in futureaccesses of the data. In some embodiments of the present invention, thedetermination regarding recycling is made based upon a frequency atwhich the data is accessed in addition to the iterative count.

Various embodiments of the present invention provide data processingsystems that include: a memory device, a data decoder circuit, and arecycle control circuit. The memory device is operable to maintain adata set, and the data decoder circuit is operable to apply one or moreiterations of a data decoding algorithm to the data set accessed fromthe memory device to yield a decoded output, and to provide an iterationcount indicating a number of iterations that the data decoding algorithmwas applied to the data set. The recycle control circuit is operable torecycle a read data corresponding to the data set. The recycle istriggered based at least in part on the iteration count.

In some instances of the aforementioned embodiments, the data decodingalgorithm is a low density parity check decoding algorithm. In variousinstances of the aforementioned embodiments, at least the data decodercircuit and the recycle control circuit are incorporated in anintegrated circuit. In some such embodiments, the memory device isfurther incorporated in the integrated circuit. In some cases, thememory device is a flash memory device. In particular cases, the flashmemory device is able to hold multiple bits of data in each memory cellof the flash memory device.

In various instances of the aforementioned embodiments, the recyclecontrol circuit includes a comparator circuit operable to compare theiteration count with a threshold level. In some such instances, thethreshold level is programmable. In other such instances, the thresholdlevel is fixed.

In one or more instances of the aforementioned embodiments, the systemsfurther include a memory access circuit. The memory access circuitoperable to: access the data set from the memory device; and calculate afrequency of access corresponding to the data set. In some suchinstances, the recycle is triggered based at least in part on theiteration count and the frequency of access. In various cases, therecycle control circuit include a comparator circuit operable to comparethe iteration count with one of a first threshold level or a secondthreshold level. The first threshold level is selected when thefrequency of access exceeds a third threshold level, and the secondthreshold level is selected when the frequency of access is less thanthe third threshold level. In particular cases, one or more of the firstthreshold level, the second threshold level and/or the third thresholdlevel is/are user programmable. In other cases, all of the firstthreshold level, the second threshold level and the third thresholdlevel are fixed.

Other embodiments of the present invention provide methods for datarecycling control in a memory device. The methods include: receiving adata set maintained in a memory device; applying at least one iterationof a data decoding algorithm to the data set by a data decoder circuitto yield a decoded output; counting the number of iterations of the datadecoding algorithm applied to the data set to yield an iteration count;and recycling the data set to the memory device such that the recyclingis triggered based at least in part on the iteration count. In someinstances of the aforementioned embodiments, the data decoding algorithmis a low density parity check decoding algorithm.

In various instances of the aforementioned embodiments, recycling thedata set is controlled by a recycle control circuit that includes acomparator circuit operable to compare the iteration count with athreshold level. In some instances of the aforementioned embodiments,the method further include determining a frequency of accesscorresponding to the data set. In some such instances, the recycle istriggered based at least in part on the iteration count and thefrequency of access.

In one or more instances of the aforementioned embodiments, recyclingthe data set is controlled by a recycle control circuit that includes acomparator circuit operable to compare the iteration count with aniteration count threshold. In some such instances, the methods furtherinclude determining the iteration count threshold based at least in parton the frequency of access. In some cases, the iteration count thresholdis selected from either a first threshold level or a second thresholdlevel, either of which is programmable.

Turning to FIG. 1, a solid state storage device 100 including aniterative count based data recycle control circuit 180 in accordancewith various embodiments of the present invention. Storage device 100includes a host controller circuit 160 that directs read and writeaccess to flash memory cells 140. Flash memory cells 140 may be NANDflash memory cells or another type of solid state memory cells as areknown in the art.

A data write is effectuated when host controller circuit 160 provideswrite data 105 to be written along with an address 110 indicating thelocation to be written. A memory access controller 120 formats writedata 105 and provides an address 123 and an encoded write data 125 to awrite circuit 130. Write circuit 130 provides a write voltage 135corresponding to respective groupings of encoded write data 125 that isused to charge respective flash memory cells addressed by address 123.For example, where flash memory cells are two bit cells (i.e., dependingupon the read voltage, a value of ‘11’, ‘10’, ‘00’, or ‘01’ isreturned), the following voltages may be applied to store the data:

Two Bit Data Input Voltage Output ‘11’ V3 ‘10’ V2 ‘00’ V1 ‘01’ V0Where V3 is greater than V2, V2 is greater than V1, and V1 is greaterthan V0.

A data read is effectuated when host controller circuit 160 providesaddress 110 along with a request to read data from the correspondinglocation in flash memory cells 140. Memory access controller 120accesses a read voltage 145 from locations indicated by address 123 andcompares the voltage to a number of threshold values to reduce thevoltage to a multi-bit read data 155. Using the same two bit example,the following multi-bit read data 155 results:

Voltage Input Two Bit Data Output >V2 ‘11’ >V1 ‘10’ >V0 ‘00’ <=V0  ‘01’This multi-bit read data 155 is provided from memory access controller120 to iterative data processing circuit 170 as read data 107. Iterativedata processing circuit 170 determines whether there are any errors inread data 107. Where there are no errors in read data 107, iterativedata processing circuit 170 provides read data 107 as read data 175, andprovides a zero value as an iterative count 179. It should be noted thatthe aforementioned table is merely an example, and that differentdevices may assign different bit values to the different voltagethresholds. For example in other cases the values in the following tablemay be used:

Voltage Input Two Bit Data Output >V2 ‘01’ >V1 ‘00’ >V0 ‘10’ <=V0  ‘11’Of course, other bit patterns may be assigned to different thresholds.

Where errors remain, iterative data processing circuit 170 generates oraccesses soft data corresponding to read data 107. Such soft dataindicates a probability that given elements of read data 107 arecorrect. In some cases, this soft data is provided by read circuit 150as soft data 154 and indicates a difference between read voltage 145 anda threshold value for the elements of read data 155. This softinformation is provided to iterative data processing circuit 170 as softdata 174. In other embodiments of the present invention, the soft datais not available from read circuit 150. In such embodiments, the softdata may be generated. Such generation of soft data may be done usingany approach known in the art for generating soft data. As one example,generation of soft data may be done similar to that disclosed in U.S.patent application Ser. No. 14/047,423 entitled “Systems and Methods forEnhanced Data Recovery in a Solid State Memory System”, and filed by Xiaet al. on Oct. 7, 2013. The entirety of the aforementioned applicationis incorporated herein by reference for all purposes.

Iterative data processing circuit 170 repeatedly applies a data decodingalgorithm to read data 107 and soft data 174 to yield a decoded output.As each iteration of the data decoding algorithm is applied, aniteration count is incremented. Where the decoded output converges(i.e., results in a correction of all remaining errors in read data107), the decoded output is provided as read data 175, and the iterationcount is provided as iterative count 179. Where the decoded output failsto converge (i.e., errors remain in the decoded output), anotheriteration of the data decoding algorithm is applied to read data 107guided by the previous decoded output to yield an updated decodedoutput. This process continues until either all errors are corrected ora timeout condition occurs (e.g., 100 iterations). In some embodimentsof the present invention, the data decoding algorithm is a low densityparity check algorithm as is known in the art. Based upon the disclosureprovided herein, one of ordinary skill in the art will recognize avariety of data decoding algorithms that may be used in relation tovarious embodiments of the present invention.

Iterative count based data recycle control circuit 180 determineswhether to recycle read data 175. Such recycling includes re-writingread data 175 to a new location in flash memory cells 140 or re-writingdata back to the same location in flash memory cells. This operates torefresh the data in flash memory cells 140 such that errors due to timedecay or cell decay (together referred to as “data decay”). Thedetermination of whether to recycle read data 175 is based uponiterative count 179. As a general rule, the value of iterative count 179increases as data decay increases. Thus, where iterative count 179exceeds a threshold value, iterative count based data recycle controlcircuit 180 causes read data 175 to be recycled by asserting a recycleenable 187 to memory access controller circuit 120. Such an approach torecycle control reduces the impact of data decay on data access latencyand/or data loss.

In some embodiments of the present invention, recycle control is furtherapplied to decrease access latency to frequently accessed data sets. Insuch a case, memory access controller circuit 120 maintains a tableindicating the frequency at which data sets are accessed from flashmemory cells 140. Information from the table is provided as a frequencyindicator 177 to iterative count based data recycle control circuit 180.This information may be used to modify the threshold value to whichiterative count 179 is compared. In particular, where frequencyindicator exceeds a threshold level (i.e., indicating read data 175 is afrequently accessed data set), the threshold value to which iterativecount 179 is compared is reduced. Thus, for frequently accessed datasets, the number of iterations allowed through iterative data processingcircuit 170 is reduced. This decreases access latency for frequentlyaccessed data sets, while allowing for greater access latency for lessfrequency accessed data sets. Such an approach to recycle controlreduces the average access latency.

Turning to FIG. 2, one implementation of an iterative data processingcircuit 200 is shown that may be used in relation to embodiments of thepresent invention. Where iterative data processing circuit 200 is usedin place of iterative data processing circuit 170 of FIG. 1, read data107 is connected to a memory data 205 input, iterative count 179 isconnected to an iteration count 296, and read data 175 is connected to ahard decision output 292.

Iterative data processing circuit 200 receives memory data 205. A softinformation access or generation circuit 214 is operable to eitheraccess soft information corresponding to memory data 205 or generatesoft information corresponding to memory data 205. Such soft informationindicates a probability that given elements of memory data 205 arecorrect. In some cases, this soft information is provided by a solidstate memory device as an input (not shown) to soft information accessgeneration circuit 214. In other cases, the soft information isgenerated. Such generation of soft information may be done using anyapproach known in the art for generating soft data. As one example,generation of soft information may be done similar to that disclosed inU.S. patent application Ser. No. 14/047,423 entitled “Systems andMethods for Enhanced Data Recovery in a Solid State Memory System”, andfiled by Xia et al. on Oct. 7, 2013. The entirety of the aforementionedapplication was previously incorporated herein by reference for allpurposes.

Soft information access or generation circuit 214 provides a combinationof soft information and memory data 205 to a central memory circuit 250as a data set 225. Once a decoder circuit 270 is available, a previouslystored data set 225 is accessed from central memory circuit 250 as adecoder input 252. In some embodiments of the present invention, thedecoder circuit 270 is a low density parity check decoder circuit as isknown in the art. Based upon the disclosure provided herein, one ofordinary skill in the art will recognize a variety of decoder circuitsthat may be used in relation to various embodiments of the presentinvention.

Decoder circuit 270 applies a data decoding algorithm to decoder input252 to yield a decoded output 271. Each time the data decoding algorithmis applied, decoder circuit 270 asserts an iteration complete indicator273 to an iteration counter circuit 295. Iteration counter circuit 295counts each time iteration complete indicator 273 is asserted andprovides iteration count 296 indicating the number of iterations throughdecoder circuit 270. Where decoded output 271 fails to converge (i.e.,decoded output 271 includes errors), another iteration of the datadecoding algorithm is applied to decoder input 252 guided by decodedoutput 271. This process is repeated until either decoded output 271converges (i.e., is error free) or a timeout condition is met.

Alternatively, where decoded output 271 converges, it is provided as adecoded output 272 to a hard decision buffer circuit 290. Hard decisionbuffer circuit 290 provides the hard decisions of decoded output 272 asa hard decision output 292. At this juncture, iteration count 296indicates the total number of iterations through decoder circuit 270that were used to correct errors in memory data 205.

Turning to FIGS. 3a-3b , flow diagrams 300, 301 showing a method foriteration count based data recycling in accordance with some embodimentsof the present invention. Following flow diagram 300 of FIG. 3a , it isdetermined whether a read request is received (block 305). Where a readrequest is not received (block 305), it is determined whether a writerequest has been received (block 395). Where a write request is received(block 395), data received is formatted and written to a location in theflash memory indicated by an address received as part of the writerequest (block 397), and the process returns to block 305.

Alternatively, when a read access is received, it includes an addressindicating a location from which the data is to be accessed. Data isthen accessed from the flash memory at the location indicated by theread request (block 310). It is determined whether the retrieved data iserror free (block 320). Where it is determined that the data is errorfree (block 320), the retrieved data is provided as read data (block325) and an iteration count is equal to zero (block 330). The processthen returns to block 305. As discussed below in relation to FIG. 3b-3c, flow diagrams 301, 302 disclose alternative parallel processestriggered anytime read data is provided.

Otherwise, where it is not determined that the data is error free (block320), soft information corresponding to the accessed data is eitheraccessed or generated (block 335). Such soft information indicates aprobability that given elements of the accessed data are correct. Insome cases, this soft information is provided by a solid state memorydevice from which the data was accessed. In other cases, the softinformation is generated. Such generation of soft information may bedone using any approach known in the art for generating soft data. Asone example, generation of soft information may be done similar to thatdisclosed in U.S. patent application Ser. No. 14/047,423 entitled“Systems and Methods for Enhanced Data Recovery in a Solid State MemorySystem”, and filed by Xia et al. on Oct. 7, 2013. The entirety of theaforementioned application was previously incorporated herein byreference for all purposes.

The accessed data and the corresponding soft information is stored as adata set to a central memory (block 340), and the iteration count isincremented to a value of one (block 345). It is then determined whetherthe data decoder circuit is available for processing (block 350). Wherethe data decoder circuit is available for processing (block 350), apreviously stored data set is accessed from the central memory as adecoder input (block 355). A data decoding algorithm is applied to theaccessed data set to yield a decoded output (block 360). Where available(i.e., for the second and later iterations), a previous decoded outputis used to guide application of the data decoding algorithm. In someembodiments of the present invention, the data decoding algorithm is alow density parity check decoding algorithm as are known in the art.Based upon the disclosure provided herein, one of ordinary skill in theart will recognize a variety of data decoding algorithms that may beused in relation to different embodiments of the present invention.

It is determined whether the decoded output converged (block 365). Whereit is determined that the decoded output converged (block 365), thedecoded output is provided as read data (block 370) and the currentiteration count is reported as the iteration count (block 385). Theprocess then returns to block 305. Again, as discussed below in relationto FIG. 3b-3c , flow diagrams 301, 302 disclose alternative parallelprocesses triggered anytime read data is provided.

Alternatively, where it is determined that the decoded output failed toconverge (block 365). It is determined whether another iteration of thedata decoding algorithm is allowed (block 375). In some cases, a maximumnumber of iterations of the data decoding algorithm is fixed orprogrammable. This is effectively a timeout condition. In some cases,the maximum number of allowable iterations of the data decodingalgorithm is one hundred. Based upon the disclosure provided herein, oneof ordinary skill in the art will recognize other numbers of iterationsthat may be allowed in relation to different embodiments of the presentinvention. Where another local iteration is not allowed (block 375), anerror is indicated (block 380) and the current iteration count isreported as the iteration count (block 385). The process then returns toblock 305. Otherwise, where another iteration of the decoding algorithmis allowed (block 375), the iteration count is incremented (block 390)and the processes of blocks 360-375 are repeated.

Turning to FIG. 3b , a flow diagram 301 shows a method in accordancewith some embodiments of the present invention for determining a datarecycle. Following flow diagram 301, it is determined whether read datahas been provided (block 303). As discussed above, read data is providedas part of blocks 325, 370 of flow diagram 300. Where read data has beenprovided (block 303), it is determined whether the access frequency ofthe read data exceeds a threshold A (block 307). The access frequency isan indication of how many time the particular data provided as read datahas been accessed from the flash memory. The access frequency may bedetermined over a defined period such as, for example, a one day period.Based upon the disclosure provided herein, one of ordinary skill in theart will recognize a variety of periods over which an access frequencymay be calculated, and/or a variety of methods for calculating theaccess frequency. In some embodiments of the present invention, thethreshold A is a fixed value. In other embodiments of the presentinvention, the threshold A is a user programmable value.

Where the access frequency exceeds threshold A (block 307), it isdetermined whether the iteration count corresponding to the providedread data exceeds a threshold B (block 309). Where the threshold B isnot exceeded (block 309), no data recycle is instigated and the processreturns to block 303. Alternatively, where the threshold B is exceeded(block 309), the provided read data is recycled (block 311). The processthen returns to block 303. Such recycling includes re-writing theprovided read data to a new location in the flash memory or to the samelocation in the flash memory. This operates to refresh the data in theflash memory such that data decay is not allowed to increase the numberof iterations of the data decoding algorithm required to correct theerrors in the data. Such an approach to recycle control reduces theimpact of data decay on data access latency and/or data loss. In someembodiments of the present invention, the threshold B is a fixed value.In other embodiments of the present invention, the threshold B is a userprogrammable value.

Alternatively, where the access frequency is not greater than thethreshold A (block 307), it is determined whether the iteration count isgreater than a threshold C (block 313). Where the iteration count isgreater than the threshold C (block 313), the provided read data isrecycled (block 311). The process then returns to block 303. Otherwise,where the iteration count is not greater than the threshold C (block313), no data recycle is instigated and the process returns to block303. In some embodiments of the present invention, the threshold C is afixed value. In other embodiments of the present invention, thethreshold C is a user programmable value.

Turning to FIG. 3c , a flow diagram 302 shows another method inaccordance with some embodiments of the present invention fordetermining a data recycle. Following flow diagram 302, it is determinedwhether read data has been provided (block 304). As discussed above,read data is provided as part of blocks 325, 370 of flow diagram 300.Where read data has been provided (block 304), it is determined whetherthe iteration count is greater than a threshold A (block 306). Where theiteration count is greater than the threshold A (block 306), theprovided read data is recycled (block 308). The process then returns toblock 304. Such recycling includes re-writing the provided read data toa new location in the flash memory or to the same location in the flashmemory. This operates to refresh the data in the flash memory such thatdata decay is not allowed to increase the number of iterations of thedata decoding algorithm required to correct the errors in the data. Suchan approach to recycle control reduces the impact of data decay on dataaccess latency and/or data loss. In some embodiments of the presentinvention, the threshold A is a fixed value. In other embodiments of thepresent invention, the threshold A is a user programmable value.Alternatively, where the iteration count is not greater than thethreshold A (block 306), no data recycle is instigated and the processreturns to block 304

It should be noted that the various blocks discussed in the aboveapplication may be implemented in integrated circuits along with otherfunctionality. Such integrated circuits may include all of the functionsof a given block, system or circuit, or a subset of the block, system orcircuit. Further, elements of the blocks, systems or circuits may beimplemented across multiple integrated circuits. Such integratedcircuits may be any type of integrated circuit known in the artincluding, but are not limited to, a monolithic integrated circuit, aflip chip integrated circuit, a multichip module integrated circuit,and/or a mixed signal integrated circuit. It should also be noted thatvarious functions of the blocks, systems or circuits discussed hereinmay be implemented in either software or firmware. In some such cases,the entire system, block or circuit may be implemented using itssoftware or firmware equivalent. In other cases, the one part of a givensystem, block or circuit may be implemented in software or firmware,while other parts are implemented in hardware.

In conclusion, the invention provides novel systems, devices, methodsand arrangements for data processing. While detailed descriptions of oneor more embodiments of the invention have been given above, variousalternatives, modifications, and equivalents will be apparent to thoseskilled in the art without varying from the spirit of the invention.Therefore, the above description should not be taken as limiting thescope of the invention, which is defined by the appended claims.

What is claimed is:
 1. A data processing system, the system comprising:a memory device operable to maintain a data set; a data decoder circuitoperable to apply one or more iterations of a data decoding algorithm tothe data set accessed from the memory device to yield a decoded output,and to provide an iteration count indicating a number of iterations thatthe data decoding algorithm was applied to the data set; a memory accesscircuit operable to calculate a frequency of access corresponding to thedata set; and a recycle control circuit including a comparator circuitoperable to compare the frequency of access with an access frequencythreshold, and the recycle control circuit modifies an iterationthreshold upon determining the frequency of access exceeds the accessfrequency threshold; wherein the comparator circuit is operable tocompare the iteration count to the modified iteration threshold; andwherein the recycle control circuit recycles read data corresponding tothe data set upon determining the iteration count exceeds the modifiediteration threshold.
 2. The data processing system of claim 1, whereinthe data decoding algorithm is a low density parity check decodingalgorithm.
 3. The data processing system of claim 1, wherein the systemfurther comprises: the memory access circuit operable to access the dataset from the memory device; wherein the recycle is triggered based atleast in part on the iteration count and the frequency of access.
 4. Thedata processing system of claim 1, wherein at least one of the iterationthreshold, the modified iteration threshold and the access frequencythreshold is user programmable.
 5. The data processing system of claim1, wherein at least the data decoder circuit and the recycle controlcircuit are incorporated in an integrated circuit.
 6. The dataprocessing system of claim 1, wherein the data processing system isimplemented on an integrated circuit.
 7. The data processing system ofclaim 1, wherein the memory device is a flash memory device.
 8. The dataprocessing system of claim 7, wherein the flash memory device is able tohold multiple bits of data in each memory cell of the flash memorydevice.
 9. A method for data recycling control in a memory device, themethod comprising: receiving a data set maintained in a memory device;applying at least one iteration of a data decoding algorithm to the dataset by a data decoder circuit to yield a decoded output; counting thenumber of iterations of the data decoding algorithm applied to the dataset to yield an iteration count; calculating a frequency of accesscorresponding to the data set; modifying an iteration threshold upondetermining the frequency of access exceeds an access frequencythreshold; comparing the iteration count with the modified iterationthreshold; and recycling read data corresponding to the data set upondetermining the iteration count exceeds the modified iterationthreshold.
 10. The method of claim 9, wherein the data decodingalgorithm is a low density parity check decoding algorithm.
 11. Themethod of claim 9, wherein the recycle is triggered based at least inpart on the iteration count and the frequency of access.
 12. The methodof claim 9, wherein the method further comprises: programming at leastone of the iteration threshold, the modified iteration threshold, andthe access frequency threshold.
 13. A data storage device, the datastorage device comprising: a flash memory device operable to maintain adata set; a memory access circuit operable to: access the data set fromthe memory device; and calculate a frequency of access corresponding tothe data set; a data decoder circuit operable to apply one or moreiterations of a data decoding algorithm to the data set accessed fromthe memory device to yield a decoded output, and to provide an iterationcount indicating a number of iterations that the data decoding algorithmwas applied to the data set; a recycle control circuit including acomparator circuit operable to compare the frequency of access with anaccess frequency threshold, the recycle control circuit modifies aniteration threshold upon determining the frequency of access exceeds theaccess frequency threshold; wherein the comparator circuit is operableto compare the iteration count to the modified iteration threshold; andwherein the recycle control circuit recycles read data corresponding tothe data set upon determining the iteration count exceeds the modifiediteration threshold.